When producing a non-woven web of synthetic fibers, a plurality of extruded fiber strands have to be deposited as evenly as possible to form a textile fabric. The fiber strands are drawn off using a feed fluid, more or less after the extrusion and cool-down processes, and are guided to a deposit belt. The distribution of the fibers on the deposit belt is preferably desired to be such that the non-woven web formed therefrom has uniform strength both in the machine direction (MD) and in the cross direction (CD). For controlling the deposition of the fibers, it is known to insert guidance elements in the region of a guidance distance, which can be adjusted between the draw-off nozzle and the deposit belt. Guidance elements of this type influence the guidance of the fibers up to their deposition on the surface of the deposit belt.
Thus, for example, an apparatus and a method are disclosed in the European Patent Specification EP 1 138 813 A1, in which method the guidance elements are designed as side walls and are arranged to form a guidance channel, which expands in a V-shaped manner towards the deposit belt. Between the guidance channel and the drawing unit there is an open space, the linear extension of which is selected such that the air blasts discharged from the draw-off nozzles can enter into the opening of the guidance channel in a substantially straight manner. The fibers are guided through the guidance channel for stretching and depositing them on the deposit belt, the depositing pattern of the fibers being determined by the shape and the air conduction inside the guidance channel. Thus, this method results in uniform deposit ellipses of the fibers on the surface of the deposit belt. Irregularities can develop in the non-woven web in the form of lumps due to large deflections of the filament curtain in the machine direction.
The apparatus disclosed in EP 1 138 813 B1 relates to a so-called melt-blown process in which the freshly extruded fibers are drawn off immediately by a hot air blast of the drawing unit discharged from the nozzle capillary. For the purpose of cooling the fibers, the latter are thus initially guided immediately through an open space in which the ambient air can be used for cooling the fibers. In order to achieve a thorough stretching of the fiber strands, the guidance distance from the drawing unit up to the deposit belt is substantially determined by the guidance channel.
If the fibers are initially cooled down after the melt-spinning and are received in the solid state through a drawing unit, and are blown for being deposited on the deposit belt, the guidance channel can be formed by the guidance elements over the entire length of the guidance distance. An apparatus of this type is disclosed in EP 1 340 842 A1 by way of example. Here, the fibers are guided inside the guidance distance through several guidance elements arranged to form a guidance channel. The guidance channel comprises several channel constrictions, which create a diffuser effect. Diffusers of this type lead to a restriction of the mobility of the fibers with the result that relatively small deposit ellipsis of the fiber strands are formed on the surface of the deposit belt. In order to, in spite of this, create the most uniform non-woven web possible, the exhaust equipment disposed beneath the deposit belt includes several sections for the purpose of discharging the air blast, thereby ensuring that the fibers rest on the deposit belt in a stable manner. However, such a measure enables only a small degree of control over the guidance of the fibers up to their deposition on the surface of the deposit belt. In this respect, it is thus only possible to achieve fiber deposits with relatively small deposit ellipses. Another disadvantage of closed systems of this type is that due to the guided flow, it is necessary to maintain longer stretching zones and thus larger distances between the draw-off nozzle and the deposit belt.
In order to control the deposit of the synthetic fibers on the deposit belt, it is further known to arrange a guidance elements in the open space formed between the draw-off nozzle and the deposit belt wherein the guidance elements can be used to change the fiber stream for the purpose of controlling the deposition of the fibers. An apparatus of this type is disclosed in US 2002/0158362 A1 by way of example. The guidance elements are held at a large distance from the deposit belt in order to create an air swirl for forming a traversing movement of the fibers. Although this helps achieve special effects in the deposit of the non-woven web, this apparatus greatly loses its effectiveness at higher production speeds.